Pyrotechnic tracer

ABSTRACT

A tracer having a pyrotechnic charge as designed for locating and guiding missiles of different types, comprising a casing which accommodates the pyrotechnic charge and a plate covering the charge and serving as a radiation emitter. The pyrotechnic charge comprises a portion which serves to heat the emitting plate to incandescence and a portion which is capable of producing the destruction of said plate as a result of a rise in temperature. The tracer thus has both the properties of a plate tracer and of a flame tracer.

United States Patent [72] Inventors Jean Marie Bouisse PoudrerieNationale de, Bont de Buis; Franck Villey Desmeserets, PoudrerieNationale de, St-Chamas, both of France [21] Appl. No. 885,113

[22] Filed Dec. 15, 1969 [45] Patented Oct. 12, 1971 [54] PYROTECHNICTRACER 13 Claims, 5 Drawing Figs.

[52] U.S. Cl l02/37.8, 102/87 [51] lnt.Cl C06d 1/10 [50] Field of Search102/35, 37.8, 87, 60

[56] References Cited UNITED STATES PATENTS 3,145,657 8/1964 Shrout etal. l02/37.8 3,354,828 11/1967 Shefler et al l02/37.8 3,399,621 9/1968Schillreff l02/37.8

Primary ExaminerRobert F. Stahl Att0rney--Young & Thompson rvno'rscnmcmoss This invention relates to a pyrotechnic tracer which can beemployed especially for locating and guiding missiles or projectiles ofdifferent types.

The pyrotechnic tracers which are employed for this purpose usuallyconsist of a canister containing a pyrotechnic compound and an ignitionsystem, the complete assembly being closed by a shutter or obturatorwhich is ejected at the time of firing. Emission of the desiredradiation (in the visible, ultraviolet or infrared region) through theorifice which is uncovered by the obturator is caused by combustion ofthe pyrotechnic compound. Tracers of this type are subject in particularto the following disadvantages:

. .;I. An emission of flames and smoke which can be very substantial.

2. A substantial variation in the weight of the tracer during operationwhich is liable to result in unbalance.

, i 3. An emission of particles which have been heated to a very hightemperature, thereby giving rise to a major disadvantage in the case ofmissiles which are guided by wires and leading to the ultimatedestruction'of these latter.

4. A very appreciable loss of luminosity in the visible or infraredregion as soon as the tracer support is in motion with respect to thedetector or with respect to the observer during operation of the tracer.

- In order to circumvent the disadvantages attached to pyrotechnictracers of the aforementioned type or so-called flame tracers, oneexpedient which has been proposed consists in the use of plate tracersin which a metallic plate is placed directly in contact with thepyrotechnic charge, thereby heating the plate and converting this latterinto an emitter which producesthe desired energy radiation.

In this form of construction, the pyrotechnic charge is thus containedin a cup-shaped container which is provided with vents for the dischargeof combustion gases.

v.Plate tracers have advantageous properties in comparison with flametracers, particularly insofar as they permit removal of smoke.

-I:Iowever, as the missile travels away from the observer, the apparentareaof the plate decreases rapidly, the difficulties involved inlocating the missile at the end of travel being increased accordingly.

The main object ofthe present invention is to overcome the disadvantagesmentioned above by simple and effective means. A further object of theinvention is to permit easy industrial manufacture of the tracerand toimprove the operatingconditions of this latter.

In accordance with the invention, the tracer having a pyrotechnic chargeasdesignedfor locating and guiding different missiles, of the typecomprising a casing which accommodates the pyrotechnic charge and aplate which covers said charge and serves as a radiation emitter, ischaracterized in that the pyrotechnic charge comprises a portion whichserves to heat the emitting plate to incandescence and a portion whichis capable of producing the destruction of said plate as a result of arise in temperature.

The tracer thus has both the properties of a plate tracer and of a flametracer.

Preferably, the tracer comprises means for carrying out the successiveignition of the two charge portions considered. It is thus possible toobtain the characteristics of a plate tracer during the initial periodof operation and then, when the missile has-travelled away from theobserver, to obtain the properties of a flame tracer after destructionof the plate since the flame has an apparent surface area which isgreater than the plate, thereby facilitating location of the missile.

In an advantageous embodiment of the invention, the two portions of thecharge are juxtaposed, the first portion being disposed between thesecond portion and a firing mass, an electric igniter being adapted topenetrate into the firing mass through an opening which is formed in thecasing and which also serves as a gas discharge vent.

The combustion smoke is thus discharged at a distance from the emittingplate during combustion of the firing mass and o the first portion ofthe charge.

As a preferable feature and in order to permit coherent operation of thetracer, the interfaces of the charges correspond to the combustionfronts whichare formed from the point of ignition.

In an advantageous embodiment of the invention, the emitting plate isformed of a metal having a high-melting point such as molybdenum andtungsten and is covered with at least one added layer which modifies itsemissive power and is provided one at least part of its surface with acoating which prevents any penetration of moisture.

Further properties of the invention will become apparent from thedescription which is given hereinafter.

One advantageous embodiment of the invention is illustrated in theaccompanying drawings which are given by way of example and not in anysense by way'lof limitation, and in which:

FIG. I is a perspective diagram of the casing prior'to' assembly;

F IG.'2 is a plan view of the completely assembled tracer;

FIG. 3 is a transverse sectional view of the'tracer, this view' beingtaken along line IIIIII of FIG. 5;

FIG. 4 is a detail sectional view on a larger scale;

FIG. 5 is a horizontal sectional view taken along line V-V of FIG. 3.

It is to'be understood that the particular indications given in thefollowing description with reference to the accompanying drawings areapplicable to the case of the structure as herein described but are alsosuited to any other structures which may be derived therefrom.

Referring now to FIG. 1 of the accompanyingdrawings, it is apparent thatthe tracer which is contemplated by the invention comprises a casing Ihaving a base 2 surrounded by a ring 3 which is provided with a seriesof tongues 4.

The casing l is preferably formed of thin sheet steel (betweenthree-tenths and eight-tenths of a millimeter in a preferred applicationof the invention). The internal face of the casing which is intended toaccommodate the pyrotechnic compound or compounds is usefullyprovidedwith a thermal shield in the form of a layer 5 of polyester resin'whichis loaded with a refractory oxide powder such as zirconia, .r'nagnesia.It is thus possible by way of example to apply against the internal wallof a casing l constructed-of ordinary. shcetsteel having a thickness offive-tenths or eight-tenths of a millimeter a layer consisting of amixture which is made up of: a

parts of prepolymerized liquid polyester 30 parts of powdered magnesiaand the catalyst and the resin polymerization accelerator. The layer 5is represented diagrammatically in FIG. I by an array of dots.

However, it would clearly not constitute any departure from the scope ofthis invention to employ any other suitable material for the fabricationof the tracer canister such as phenolic compounds, other thermosettingmaterials, laminated materials or the like.

The ring 3 is pierced by an orifice 6, a panel 7 being mounted abovesaid orifice and provided on. each side with triangular tongues 8. Thepanel 7 is intended to be folded back towards the orifice 6 at 7a; thetongues 8 serve as abutment members and the complete assemblyconstitutes a deflecting shutter. That surface of the panel 7 and of thetongues 8 which is located opposite to the orifice 6 is provided with ahcat resistant coating formed of a mixture of polyester resin and arefractory oxide powder, Said coating being represented diagrammaticallyin FIG. 1 by an array of dots.

As will become apparent hereinafter, the orifice 6 serves both as alead-in passage for the electric igniter wires 9 and for the dischargeof the combustion gases during operation of the tracer.

The composite pyrotechnic charge C is set within the casing l andcovered by an emitting plate II which is applied against boron 20 partsbarium chromate 70 parts magnetic oxide of iron parts This compound inpowdered form may be bonded if necessary by a polyester resin or acollodion obtained by dissolving nitrocellulose in suitable solvents.

For example, the above compound can be agglomerated by 3 percentpolyester resin except in the immediate vicinity of the igniters whereit is left in the powdered state without binder. However, a thin layerof this mixture which is agglomerated with a collodion of nitrocelluloseis placed immediately beneath the plate 11 and opposite to the orifice 6in order that the portion which has been left in the powdered stateshould be maintained in position.

The precaution which has just been mentioned becomes unnecessary if theorifice 6 is closed by a plug of thermoplastic material or of aluminum.The igniter wires 9 are thus passed through said plug and the completeassembly is made leaktight, for example by means of a few drops ofethoxyl resin disposed around the igniter wires.

Said plug is then fixed in order to be readily ejectable as a result ofoverpressure produced by combustion of the charge C.

In particular, the plug can be fabricated from a sandwichtype materialsuch as paperboard-aluminum-polythene which is simply applied againstthe internal wall of the ring 3 and maintained in leaktight manner bythe polyester-magnesia mixture of the layer 5.

b. a portion C which is highly exothermic but the composition of whichis established in relation to the nature of the emitting plate 1 1 inorder that this latter should not burst as a result of a temperaturerise.

For example, in the case of a plate 11 formed of molybdenum, thecomposition of the portion C can be as follows:

polyester binder.

A cobalt powder is preferably incorporated in the above compound inorder to thicken the slag produced by combustion of the pyrotechniccompound or compounds employed and in order to reduce the weight loss ofthe tracer during combustion. This cobalt powder is mixed in smallquantities (usually 2 to 10 percent and advantageously 3 percent in thecase of the above example) with the pyrotechnic compound or compoundsemployed.

c. A portion C which is more highly exothermic than the previous portionand capable at the time of combustion of causing at least partialdestruction of the emitting plate 1 l as a result of a rise intemperature.

The portion C can be constituted in particular by an exothermic mixturewhich is known per se and consists of iron, aluminum and iron oxide inproportions which are close to stoichiometric.

In another example, the following composition is employed:

powdered aluminum 80 parts anhydrous calcium sulfate 130 parts, thiscompound being made more highly flammable if so required by adding asmall quantity of powdered magnesium.

Advantageous results have thus been obtained by means of the followingmixture:

anhydrous calcium sulfate 136 parts aluminum 54 parts magnesium 5 partsThe interfaces S and S which delimit the portions C,, C,, C of thecharge C are advantageously disposed along the contours of thecombustion fronts of the portions considered at a given instant in orderthat ignition of the portion C, should take place simultaneously alongthe surface 12 and similarly in the case of the portion C So far as theemitting plate 11 is concerned, a special structure is provided.

The plate 11 is advantageously fabricated from a metal having a highmelting point such as molybdenum or tungsten. In order to permit a veryrapid temperature rise, the thickness of the plate is small (for examplebetween 0.2 and 0.4 mm.) and has in fact a significant effect on therate at which the compound C heats the plate to incandescence. Thus, inthe case of a plate formed of molybdenum, incandescence is retarded byapproximately 5 seconds when the thickness is increased from 0.2 to 0.8mm.

In a preferred embodiment, the emissive power of the plate 11 isenhanced by applying to this latter by means of a spray gun eithermetals and especially iron or oxides, sulfides, carbides, nitrides,silicides and any refractory chemical compounds which have high-emissivepower and a liquid phase at atmospheric pressure so that such materialscan be applied to the metal plate 11 by means of a spray-jet appliancewhich is commonly referred to as a plasma-arc torch. Tracers which canbe mentioned by way of example are fitted with a molybdenum plate whichis metallized by spray deposition of iron or with a molybdenum platewhich is coated with cerium oxide.

in an advantageous embodiment, two different superposed coatings aredeposited on the plate 11, the object of the second coating being eitherto protect the first or to remove part of the radiation emitted by theplate 1 1.

By way of nonlimitative example, the first coating can consist of ceriumoxide and the second coating can consist of a layer of stibine (antimonytrisulfide). In another embodiment, a molybdenum plate is metallized byspraying with iron and the metallized plate is coated with calciumfluoride. Thus, good results have been obtained by means of a compositecoating as illustrated in FIG. 4 and having the following composition:

a layer 12 having a thickness of 0.] to 0.2 mm. and consisting of ceriumoxide,

a layer 13 having a thickness of 0.1 mm. and consisting of calciumfluoride or stibine or alternatively consisting of a mixture of 99percent thoria and 1 percent cerium oxide.

The substances employed for the layer 12 have a melting temperaturewhich is higher than that of the plate 11 (2,600" C in the case ofmolybdenum), an emissive power which is greater than that of the plate11 (0.32 in the case of molybdenum) and a liquid phase at atmosphericpressure so as to permit their application. Said substances must neitherdecompose not sublime. For this reason, the white and colored refractoryoxides are usually suitable as well as metals having an emissive powerwhich is higher than that of the plate 1! (iron in the case ofmolybdenum). The layer 13 makes it possible to remove part of theradiation of the layer 12 and is a function of the properties of thislatter and of the properties of the detector.

In another arrangement of the invention, at least part of the externalsurface and the edges of the plate 11 are provided with a coating 16which prevents any penetration of moisture.

By way of example, the coating 16 is advantageously constituted by avarnish having a base of silicone resins or alternatively of a siliconeelastomer.

it is apparent that the emitting plate ll which is pretreated is placedon the charge C and fixed in position by folding back the tongues 4.

The tracer as thus constituted is fixed on any ballistic missile or thelike which is to be detected by visual means. The tracer is placed sothat the observer should be permitted to see the flame or the plate withan apparent diameter which is as large as possible. As a rule, thetracer is placed either behind or at the base of the fins of themissile.

At the time of ignition, the firing mass C burns and then simultaneouslytransmits the flame along the surface S to the portion C which heats theplate 11 to incandescence. The radiation is excited by the layer 12 andfiltered if necessary by the layer 13.

The combustion gases are discharged through the orifice 6 and are forceddownwards by the panel 7a which serves as a deflector. By virtue of saidpanel, the solid particles and the gas jet which is discharged throughthe orifice 6 are prevented from passing between the plate 11 and thedetector or observer as this would disturb the detection. The refractorycoating which is deposited on the panel 7a prevents destruction of thislatter.

Afier combustion of the portion C,, the portion C of the charge isignited along the surface S, and the evolution of heat is then such thatthe plate 11 bursts. The flame is then directly detected by theobserver. The tracer behaves in the same manner as a flame tracer.

It is apparent that the invention is not limited to the embodimenthereinabove described and that many alternative forms can becontemplated.

Thus, the casing 1 can have any shape other than an oval shape.

Moreover, in order to facilitate destruction of the plate 11, provisioncan be made for a variable thickness in which that portion of the platewhich has the smallest thickness is located opposite to the portion C,of the charge C.

What we claim is:

l. A tracer having a pyrotechnic charge as designed for locating andguiding missiles of different types, comprising a casing whichaccommodates the pyrotechnic charge and a plate which covers said chargeand serves as a radiation emitter, wherein the pyrotechnic chargecomprises a portion which serves to heat the emitting plate toincandescence and a portion which is capable of producing thedestruction of said plate as a result of a rise in temperature.

2. A tracer according to claim 1, wherein said tracer comprises meansfor carrying out the successive ignition of the two charge portionsconsidered.

3. A tracer according to claim 2, wherein the two portions of the chargeare juxtaposed, the first portion being disposed between the secondportion and a firing mass.

4. A tracer according to claim 3, wherein the casing is adapted to carryan electric igniter which terminates in the firing mass.

5. A tracer according to claim 4, wherein the electric igniter isadapted to penetrate into the firing mass through an opening which isformed in the casing and which also serves as a gas discharge vent.

6. A tracer according to claim 1, wherein the interfaces of the chargescorrespond to the combustion fronts which are formed from the point ofignition after a predetermined time interval.

7. A tracer according to claim I, wherein at least part of the chargecontains cobalt powder in order to thicken the slag.

8. A tracer according to claim 1, wherein the emitting plate is formedof a metal having a high-melting point such as molybdenum and tungsten.

9. A tracer according to claim 1, wherein the emitting plate is providedwith at least one coating for modifying the emissive power thereof.

10. A tracer according to claim 9, wherein the emitting plate isprovided with two superposed coatings, the first coating being intendedto increase the emissive power of said plate and the second coatingbeing intended to perform the function of an optical filter.

11. A tracer according to claim 1, wherein the emitting plate isprovided on at least part of its surface with a coating which preventsany penetration of moisture.

12. A tracer according to claim 1, wherein the emitting plate is placedon the pyrotechnic charge and applied against said charge by means oftongues which form part of a ring of the casing and are folded backagainst said plate.

13. A tracer according to claim 1, wherein the internal surface of thecasing which is in contact with the pyrotechnic charge is provided witha coating constituted by a resin which is loaded with a refractoryproduct.

1. A tracer having a pyrotechnic charge as designed for locating andguiding missiles of different types, comprising a casing whichaccommodates the pyrotechnic charge and a plate which covers said chargeand serves as a radiation emitter, wherein the pyrotechnic chargecomprises a portion which serves to heat the emitting plate toincandescence and a portion which is capable of producing thedestruction of said plate as a result of a rise in temperature.
 2. Atracer according to claim 1, wherein said tracer comprises means forcarrying out the successive ignition of the two charge portionsconsidered.
 3. A tracer according to claim 2, wherein the two portionsof the charge are juxtaposed, the first portion being disposed betweenthe second portion and a firing mass.
 4. A tracer according to claim 3,wherein the casing is adapted to carry an electric igniter whichterminates in the firing mass.
 5. A tracer according to claim 4, whereinthe electric igniter is adapted to penetrate into the firing massthrough an opening which is formed in the casing and which also servesas a gas discharge vent.
 6. A tracer according to claim 1, wherein theinterfaces of the charges correspond to the combustion fronts which areformed from the point of ignition after a predetermined time interval.7. A tracer accorDing to claim 1, wherein at least part of the chargecontains cobalt powder in order to thicken the slag.
 8. A traceraccording to claim 1, wherein the emitting plate is formed of a metalhaving a high-melting point such as molybdenum and tungsten.
 9. A traceraccording to claim 1, wherein the emitting plate is provided with atleast one coating for modifying the emissive power thereof.
 10. A traceraccording to claim 9, wherein the emitting plate is provided with twosuperposed coatings, the first coating being intended to increase theemissive power of said plate and the second coating being intended toperform the function of an optical filter.
 11. A tracer according toclaim 1, wherein the emitting plate is provided on at least part of itssurface with a coating which prevents any penetration of moisture.
 12. Atracer according to claim 1, wherein the emitting plate is placed on thepyrotechnic charge and applied against said charge by means of tongueswhich form part of a ring of the casing and are folded back against saidplate.
 13. A tracer according to claim 1, wherein the internal surfaceof the casing which is in contact with the pyrotechnic charge isprovided with a coating constituted by a resin which is loaded with arefractory product.